i might be mistaken but i don't believe your standard toslink optical cable is the same as a glass optical cable. it's quite possible that the difference you're hearing between your dvd player and your cd player is due to the dac inside your receiver/preamp. your receiver could be adding additional processing to the optical input.
if your receiver/preamp has a "pure direct" type of mode, make sure both input that your cd and dvd player are on are set to this and give it another comparison to see. as far as trying a more expensive optical cable, i can't say i would bother, but if you can get a decent return policy on a better cable, give it a whirl.
if your receiver/preamp has a "pure direct" type of mode, make sure both input that your cd and dvd player are on are set to this and give it another comparison to see. as far as trying a more expensive optical cable, i can't say i would bother, but if you can get a decent return policy on a better cable, give it a whirl.